We are looking for advice on which fruit/veg trees are most hardy and drought resistant as well as where to purchase - for the back of our property in Florida. We are thinking maybe a tangerine and an avocado, possibly a fig?

Hi Kathy
That is a very localized question that is best addressed to people with detailed knowledge of your area.
I would begin with the local extension office from Florida University http://solutionsforyourlife.ufl.edu/
Local nurseries are also helpful